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Abstract

We demonstrate reduction of the free-carrier lifetime in a silicon nanowaveguide from 3 ns to 12.2 ps by applying a reverse bias across an integrated p-i-n diode. This observation represents the shortest free-carrier lifetime demonstrated to date in silicon waveguides. Importantly, the presence of the p-i-n structure does not measurably increase the propagation loss of the waveguide. We derive a figure of merit demonstrating equal dependency of the nonlinear phase shift on free-carrier lifetime and linear propagation loss.

Figures (5)

Cross-sectional schematic of p-i-n waveguide device. The device consists of a silicon rib waveguide on the SOI platform. The waveguide has silicon dioxide cladding, p + and n + doping in the slab region on either side, and vias and contacts to the doped regions.

Top view (a) optical microscope image and (b) schematic of p-i-n waveguide. The two outer contacts are connected to the n + region with etched vias, whereas the center contact is only connected to the p + region. The n + region underneath the p + contact is electrically isolated by a 1-µm layer of silicon dioxide.

Experimentally measured free-carrier lifetime as a function of reverse bias in silicon photonic waveguides optimized for phase matching with an integrated p-i-n diode for reduction of nonlinear loss. (a) The free-carrier concentration as a function of time for different reverse biases. (b) The measured free-carrier lifetime as a function of reverse bias, illustrating the ability to reduce the free-carrier lifetime to 12.2 ps. The lifetime for 9-V bias was measured as a function of pump power as shown in the inset.

Numerical solution of the maximum nonlinear phase shift for different values of linear propagation loss and free-carrier lifetime (circles). The blue line is plotted with a slope of –1/2 showing the consistency of the numerical solutions with the derived figure of merit [Eq. (8)]. The gray region depicts the range of linear propagation loss and free-carrier lifetime values where most silicon nanowaveguide nonlinear optical processes are performed. Note that the individual values of the free-carrier lifetime and linear propagation loss are varied by orders of magnitude, but provided that the product is constant, the maximum nonlinear phase shift is nearly identical as depicted by the multiple overlapping data points (circles) at each x value.